The present invention relates to water craft for clearing navigational waters, and in particular, but not exclusively, to a water craft for clearing the beds of navigational waters, such as rivers, canals and docks.
Most water craft of this type are relatively small, such that they are highly maneuverable in places such as rivers, canals and docks, where there is often a limited amount of space in which to move, especially if the waterway is blocked with debris. A water craft for clearing navigational waters is described in U.S. Pat. Nos. 3,326,379, 3,434,444, 4,616,588, 4,674,984 and Des. 290,351. It comprises a floating body having propulsion means and steering means, and an arm pivotally mounted above the deck of the craft on the end of which arm is mounted a scoop for clearing flotsam from the surface of the water. The arm is pivotable by means of a hydraulic ram extending between the arm and a fixed portion on the craft, and the scoop may be tilted by a hydraulic ram mounted between the arm and a fixed portion on the craft, and the scoop may be tilted by a hydraulic ram mounted between a portion of the scoop and a portion of the arm.
Such a device has been successfully used for many years, but it is known that it suffers from certain disadvantages. One such disadvantage is that the craft is suitable only for removing material from the surface of the water, or slightly below the surface, since the depth to which the scoop can be lowered is somewhat limited. A second disadvantage is that when the scoop is fully loaded, the craft is rendered unstable in the water.
One device which is able to clear the beds of navigational waters comprises a floating body, such as a barge-type craft, which has a hydraulically-actuated arm mounted on its deck, the arm being provided with a scoop at its free end. The arm is movable such that the scoop can extend to the bed of a waterway, and can be used to remove debris therefrom. Unfortunately, as the scoop lifts the debris, the craft itself is moved across the surface of the waterway due to the equal and opposite reaction force. Thus, with such a craft it is not possible to position the craft accurately in the water, and removal of debris from the bed of the waterway is also hindered by the movement of the craft. In order to overcome this disadvantage, such craft are provided with a plurality of legs or "spuds", usually one at each corner of the craft, which may be lowered onto the bed of the waterway. In use, the craft moves to a desired position and the spuds are lowered onto the bed of the waterway, thereby securing the craft in a fixed position. The arm is then manoeuvred to remove as much debris as possible from the bed in the vicinity of craft, whereupon the spuds are retracted and the craft is moved on to an adjacent position where the spuds are once again lowered into contact with the bed, and the operation is repeated.
The above craft is obviously not very maneuverable in use, since it is necessary to lower the spuds each time debris is to be removed from the bed of the waterway. Lowering and retraction of the spuds also takes time, and may require an extra operator to lower and raise them, while a different operator controls the craft to keep it in a fixed position on the waterway.